Reason's name can be not unique through update

When testing I noticed that it is possible to change a reason's name to already existing.

Reproduction steps:
1. As administrator go to Administration -> Reasons.
2. Create a new reason and name it "Receipts" - it should not be possible to do so. Try changing name to "ReCEipts" - it should also not be possible to do so. Finally, name it "ReasonTEST" or give it another unique name.
3. Click Edit next to a newly created reason and change its name to "Receipts" - it's not possible. Next change it to "ReCEipts" - it is possible.

Acceptance criteria:
1. Validation for a reason's name should be case-insensitive for all steps, creating and updating.